Tissue palpation in endoscopy using EIT and soft actuators.

The integration of soft robots in medical procedures has significantly improved diagnostic and therapeutic interventions, addressing safety concerns and enhancing surgeon dexterity. In conjunction with artificial intelligence, these soft robots hold the potential to expedite autonomous interventions, such as tissue palpation for cancer detection. While cameras are prevalent in surgical instruments, situations with obscured views necessitate palpation. This proof-of-concept study investigates the effectiveness of using a soft robot integrated with Electrical Impedance Tomography (EIT) capabilities for tissue palpation in simulated in vivo inspection of the large intestine. The approach involves classifying tissue samples of varying thickness into healthy and cancerous tissues using the shape changes induced on a hydraulically-driven soft continuum robot during palpation. Shape changes of the robot are mapped using EIT, providing arrays of impedance measurements. Following the fabrication of an in-plane bending soft manipulator, the preliminary tissue phantom design is detailed. The phantom, representing the descending colon wall, considers induced stiffness by surrounding tissues based on a mass-spring model. The shape changes of the manipulator, resulting from interactions with tissues of different stiffness, are measured, and EIT measurements are fed into a Long Short-Term Memory (LSTM) classifier. Train and test datasets are collected as temporal sequences of data from a single training phantom and two test phantoms, namely, A and B, possessing distinctive thickness patterns. The collected dataset from phantom B, which differs in stiffness distribution, remains unseen to the network, thus posing challenges to the classifier. The classifier and proposed method achieve an accuracy of 93 % and 88.1 % on phantom A and B, respectively. Classification results are presented through confusion matrices and heat maps, visualising the accuracy of the algorithm and corresponding classified tissues.

Advancing Sensing Resolution of Impedance Hand Gesture Recognition Devices.

Gestures are composed of motion information (e.g. movements of fingers) and force information (e.g. the force exerted on fingers when interacting with other objects). Current hand gesture recognition solutions such as cameras and strain sensors primarily focus on correlating hand gestures with motion information and force information is seldom addressed. Here we propose a bio-impedance wearable that can recognize hand gestures utilizing both motion information and force information. Compared with previous impedance-based gesture recognition devices that can only recognize a few multi-degrees-of-freedom gestures, the proposed device can recognize 6 single-degree-of-freedom gestures and 20 multiple-degrees-of-freedom gestures, including 8 gestures in 2 force levels. The device uses textile electrodes, is benchmarked over a selected frequency spectrum, and uses a new drive pattern. Experimental results show that 179 kHz achieves the highest signal-to-noise ratio (SNR) and reveals the most distinct features. By analyzing the 49,920 samples from 6 participants, the device is demonstrated to have an average recognition accuracy of 98.96%. As a comparison, the medical electrodes achieved an accuracy of 98.05%.

A Tension Sensor Array for Cable-Driven Surgical Robots.

Tendon-sheath structures are commonly utilized to drive surgical robots due to their compact size, flexibility, and straightforward controllability. However, long-distance cable tension estimation poses a significant challenge due to its frictional characteristics affected by complicated factors. This paper proposes a miniature tension sensor array for an endoscopic cable-driven parallel robot, aiming to integrate sensors into the distal end of long and flexible surgical instruments to sense cable tension and alleviate friction between the tendon and sheath. The sensor array, mounted at the distal end of the robot, boasts the advantages of a small size (16 mm outer diameter) and reduced frictional impact. A force compensation strategy was presented and verified on a platform with a single cable and subsequently implemented on the robot. The robot demonstrated good performance in a series of palpation tests, exhibiting a 0.173 N average error in force estimation and a 0.213 N root-mean-square error. In blind tests, all ten participants were able to differentiate between silicone pads with varying hardness through force feedback provided by a haptic device.

Transcutaneous fluorescence spectroscopy: development and characterization of a compact, portable, and fiber-optic sensor.

Significance: The integrity of the intestinal barrier is gaining recognition as a significant contributor to various pathophysiological conditions, including inflammatory bowel disease, celiac disease, environmental enteric dysfunction (EED), and malnutrition. EED, for example, manifests as complex structural and functional changes in the small intestine leading to increased intestinal permeability, inflammation, and reduced absorption of nutrients. Despite the importance of gut function, current techniques to assess intestinal permeability (such as endoscopic biopsies or dual sugar assays) are either highly invasive, unreliable, and/or difficult to perform in certain patient populations (e.g., infants). Aim: We present a portable, optical sensor based on transcutaneous fluorescence spectroscopy to assess gut function (in particular, intestinal permeability) in a fast and noninvasive manner. Approach: Participants receive an oral dose of a fluorescent contrast agent, and a wearable fiber-optic probe detects the permeation of the contrast agent from the gut into the blood stream by measuring the fluorescence intensity noninvasively at the fingertip. We characterized the performance of our compact optical sensor by comparing it against an existing benchtop spectroscopic system. In addition, we report results from a human study in healthy volunteers investigating the impact of skin tone and contrast agent dose on transcutaneous fluorescence signals. Results: The first study with eight healthy participants showed good correlation between our compact sensor and the existing benchtop spectroscopic system [correlation coefficient (r)>0.919, p<0.001]. Further experiments in 14 healthy participants revealed an approximately linear relationship between the ingested contrast agent dose and the collected signal intensity. Finally, a parallel study on the impact of different skin tones showed no significant differences in signal levels between participants with different skin tones (p>0.05). Conclusions: In this paper, we demonstrate the potential of our compact transcutaneous fluorescence sensor for noninvasive monitoring of intestinal health.

Rewriting the script: How COVID-19 affected the relation between intrinsic aspirations and depressive symptoms.

Self-determination theory proposes that intrinsic aspirations protect against negative mental health outcomes by satisfying people's basic psychological needs of autonomy, relatedness, and competence. The present study investigated this relationship using two four-wave prospective longitudinal studies which followed undergraduate students across the Canadian academic calendar (September to May). The first was conducted across 2018-19 and the second across 2019-20. By comparing these two samples, we examined whether baseline levels of intrinsic aspirations moderated the impact of the COVID-19 pandemic on the development of depressive symptoms. Three main findings emerged, the first being that students reported higher levels of depressive symptoms in Spring 2020 than in Spring 2019. Second, students with more intrinsic aspirations in the pre-pandemic sample (2018-19) experienced fewer depressive symptoms from December to May while students with more intrinsic aspirations in the pandemic sample (2019-20) experienced more depressive symptoms during this period. Lastly, the latter relationship was mediated by need frustration, whereby students with higher levels of intrinsic aspirations experienced greater need frustration during the pandemic year. Together, these findings suggest that although intrinsic aspirations typically protect against negative psychological outcomes, the unique need frustrating context of the pandemic made them a risk factor for depression.

Non-invasive assessment of intestinal permeability in healthy volunteers using transcutaneous fluorescence spectroscopy.

The permeability of the intestinal barrier is altered in a multitude of gastrointestinal conditions such as Crohn's and coeliac disease. However, the clinical utility of gut permeability is currently limited due to a lack of reliable diagnostic tests. To address this issue, we report a novel technique for rapid, non-invasive measurement of gut permeability based on transcutaneous ('through-the-skin') fluorescence spectroscopy. In this approach, participants drink an oral dose of a fluorescent dye (fluorescein) and a fibre-optic fluorescence spectrometer is attached to the finger to detect permeation of the dye from the gut into the blood stream in a non-invasive manner. To validate this technique, clinical trial measurements were performed in 11 healthy participants. First, after 6 h of fasting, participants ingested 500 mg of fluorescein dissolved in 100 ml of water and fluorescence measurements were recorded at the fingertip over the following 3 h. All participants were invited back for a repeat study, this time ingesting the same solution but with 60 g of sugar added (known to transiently increase intestinal permeability). Results from the two study datasets (without and with sugar respectively) were analysed and compared using a number of analysis procedures. This included both manual and automated calculation of a series of parameters designed for assessment of gut permeability. Calculated values were compared using Student's T-tests, which demonstrated significant differences between the two datasets. Thus, transcutaneous fluorescence spectroscopy shows promise in non-invasively discriminating between two differing states of gut permeability, demonstrating potential for future clinical use.

Vascular, cardiac, and renal lesions attributed to primary systemic hypertension in western pygmy marmosets (Cebuella pygmaea).

In a retrospective study of a western pygmy marmoset (Cebuella pygmaea) colony, postmortem examination of 1/8 juvenile and 29/47 adult animals identified vascular, cardiac, and renal lesions consistent with systemic hypertension. This included frequent renal arteriolar hypertrophy, hyaline and proliferative arteriolosclerosis, fibrinoid necrosis of arterioles, glomerulosclerosis, and nephrosclerosis. Affected animals ranged from 0.6 to 12 years of age (mean 6 years) and had an observed male predominance. Genealogical relatedness was evident in several breeding pairs and spanned multiple generations. Concurrent cardiac and renal disease was commonly identified, although frequently subclinical, and both were important causes of morbidity and mortality in affected animals. Cardiomegaly and hypertrophy were typical features and were accompanied by left atrial thrombosis in 10 animals. Signs of heart failure included chronic pulmonary edema in 20 cases and body cavity effusions in 17. In the kidneys, 19 cases had glomerular disease and hypertensive vasculopathy, and 26 cases had nephrosclerosis or glomerulosclerosis. Common extrarenal secondary causes of hypertension were excluded by necropsy examination. The pathogenesis is suggested to involve primary hypertension leading to renal and cardiac disease. Elevated sympathetic activity might be an underlying factor in the frequent development of primary systemic hypertension in the pygmy marmoset, as for the owl monkey.

Simulating fullerene polyhedral formation from planar precursors.

The synthesis path of the C60-Buckyball fullerene from a planar precursor developed by Scott et al. [Science, 2002, 295, 5559] is investigated with density functional theory (DFT) methods. Various theoretically possible closing paths are analysed with respect to structural and energetic properties. The initial geometries were obtained by geometric interpolation of a cardboard-like model comprising rigid rings connected by hinges, which were then fully optimized with a selection of DFT-functionals. Analysis of the fully optimised geometries shows remarkable stability of face planarity, bond lengths and bond angles for all studied geometries, indicating soundness of the "cardboard with hinges"-model for approximating reaction paths for molecules of this type. This raises hope for development of a force field description of fullerene precursor molecules that can aid in discovery and analysis of good precursor candidates for rational synthesis of new fullerenes.

Imaging slow brain activity during neocortical and hippocampal epileptiform events with electrical impedance tomography.

OBJECTIVE: Electrical impedance tomography (EIT) is an imaging technique that produces tomographic images of internal impedance changes within an object using surface electrodes. It can be used to image the slow increase in cerebral tissue impedance that occurs over seconds during epileptic seizures, which is attributed to cell swelling due to disturbances in ion homeostasis following hypersynchronous neuronal firing and its associated metabolic demands. In this study, we characterised and imaged this slow impedance response during neocortical and hippocampal epileptiform events in the rat brain and evaluated its relationship to the underlying neural activity. APPROACH: Neocortical or hippocampal seizures, comprising repeatable series of high-amplitude ictal spikes, were induced by electrically stimulating the sensorimotor cortex or perforant path of rats anaesthetised with fentanyl-isoflurane. Transfer impedances were measured during ≥30 consecutive seizures, by applying a sinusoidal current through independent electrode pairs on an epicortical array, and combined to generate an EIT image of slow activity. MAIN RESULTS: The slow impedance responses were consistently time-matched to the end of seizures and EIT images of this activity were reconstructed reproducibly in all animals (p < 0.03125, N = 5). These displayed foci of activity that were spatially confined to the facial somatosensory cortex and dentate gyrus for neocortical and hippocampal seizures, respectively, and encompassed a larger volume as the seizure progressed. Centre-of-mass analysis of reconstructions revealed that this activity corresponded to the true location of the epileptogenic zone, as determined by EEG recordings and fast neural EIT measurements which were obtained simultaneously. SIGNIFICANCE: These findings suggest that the slow impedance response presents a reliable marker of hypersynchronous neuronal activity during epileptic seizures and can thus be utilised for investigating the mechanisms of epileptogenesis in vivo and for aiding localisation of the epileptogenic zone during presurgical evaluation of patients with refractory epilepsies.

Self-Abrading Servo Electrode Helmet for Electrical Impedance Tomography.

Electrical Impedance Tomography (EIT) is a medical imaging technique which has the potential to reduce time to treatment in acute stroke by rapidly differentiating between ischaemic and haemorrhagic stroke. The potential of these methods has been demonstrated in simulation and phantoms, it has not yet successfully translated to clinical studies, due to high sensitivity to errors in scalp electrode mislocation and poor electrode-skin contact. To overcome these limitations, a novel electrode helmet was designed, bearing 32 independently controlled self-abrading electrodes. The contact impedance was reduced through rotation on an abrasive electrode on the scalp using a combined impedance, rotation and position feedback loop. Potentiometers within each unit measure the electrode tip displacement within 0.1 mm from the rigid helmet body. Characterisation experiments on a large-scale test rig demonstrated that approximately 20 kPa applied pressure and 5 rotations was necessary to achieve the target 5 kΩ contact impedance at 20 Hz. This performance was then replicated in a simplified self-contained unit where spring loaded electrodes are rotated by servo motors. Finally, a 32-channel helmet and controller which sequentially minimised contact impedance and simultaneously located each electrode was built which reduced the electrode application and localisation time to less than five minutes. The results demonstrated the potential of this approach to rapidly apply electrodes in an acute setting, removing a significant barrier for imaging acute stroke with EIT.

Optimised induction of on-demand focal hippocampal and neocortical seizures by electrical stimulation.

BACKGROUND: Epilepsy is a common neurological disorder affecting over 60 million people globally, approximately a third of whom are refractory to pharmacotherapy. Surgical resection of the epileptogenic zone is frequently unsuitable or ineffective, particularly for individuals with focal neocortical or mesial temporal lobe epilepsy. Therefore, there is a need to develop animal models for elucidating the mechanisms of focal epilepsies and evaluating novel treatment strategies. NEW METHOD: We present two adapted in vivo seizure models, the neocortical and hippocampal epileptic afterdischarge models, that enable stereotyped seizures to be induced on demand by electrical stimulation in anaesthetised, neurologically intact rats. The stimulation parameters and anaesthetic were optimised to generate electrographically reproducible, self-sustaining seizures with a well-defined focal origin. RESULTS: Neocortical or hippocampal seizures were consistently generated under fentanyl-isoflurane anaesthesia by stimulating the sensorimotor cortex or perforant path, respectively, with 100 Hz trains of biphasic square-wave pulses. The induced seizures were suppressed by propofol, an established antiseizure anaesthetic, thus validating the clinical responsiveness of the developed models. COMPARISON WITH EXISTING METHODS: The high degree of reproducibility in seizure presentation, predictable seizure induction and ability to operate in anaesthetised animals renders these models overall less laborious and more cost-effective than most conventionally used seizure models. CONCLUSIONS: The proposed models provide an efficient method for the high-throughput screening of novel antiseizure therapies, including closed-loop stimulation paradigms, and are well-suited to in vivo investigations that require tight regulation of seizure timing under anaesthetised conditions, particularly neuroimaging studies aimed at understanding the development of epileptogenic networks.

Multi-frequency symmetry difference electrical impedance tomography with machine learning for human stroke diagnosis.

OBJECTIVE: Multi-frequency symmetry difference electrical impedance tomography (MFSD-EIT) can robustly detect and identify unilateral perturbations in symmetric scenes. Here, an investigation is performed to assess if the algorithm can be successfully applied to identify the aetiology of stroke with the aid of machine learning. METHODS: Anatomically realistic four-layer finite element method models of the head based on stroke patient images are developed and used to generate EIT data over a 5 Hz-100 Hz frequency range with and without bleed and clot lesions present. Reconstruction generates conductivity maps of each head at each frequency. Application of a quantitative metric assessing changes in symmetry across the sagittal plane of the reconstructed image and over the frequency range allows lesion detection and identification. The algorithm is applied to both simulated and human (n = 34 subjects) data. A classification algorithm is applied to the metric value in order to differentiate between normal, haemorrhage and clot values. MAIN RESULTS: An average accuracy of 85% is achieved when MFSD-EIT with support vector machines (SVM) classification is used to identify and differentiate bleed from clot in human data, with 77% accuracy when differentiating normal from stroke in human data. CONCLUSION: Applying a classification algorithm to metrics derived from MFSD-EIT images is a novel and promising technique for detection and identification of perturbations in static scenes. SIGNIFICANCE: The MFSD-EIT algorithm used with machine learning gives promising results of lesion detection and identification in challenging conditions like stroke. The results imply feasible translation to human patients.

In vivo imaging of deep neural activity from the cortical surface during hippocampal epileptiform events in the rat brain using electrical impedance tomography.

Electrical impedance tomography (EIT) is a medical imaging technique which reconstructs images of the internal impedance changes within an object using non-penetrating surface electrodes. To date, EIT has been used to image fast neural impedance changes during somatosensory evoked potentials and epileptiform discharges through the rat cerebral cortex with a resolution of 2 â€‹ms and <300 â€‹µm. However, imaging of neural activity in subcortical structures has never been achieved with this technique. Here, we evaluated the feasibility of using EIT to image epileptiform activity in the rat hippocampus using non-penetrating electrodes implanted on the cortical surface. Hippocampal epileptiform events, comprising repetitive 30-50 â€‹Hz ictal spikes, were induced by electrically stimulating the perforant path of rats anaesthetised with fentanyl-isoflurane. For each of ≥30 seizures, impedance measurements were obtained by applying 100 â€‹µA current at 1.4 â€‹kHz through an independent pair of electrodes on a 54-electrode planar epicortical array and recording boundary voltages on all remaining electrodes. EIT images of averaged ictal spikes were reconstructed using impedance recordings from all seizures in each animal. These revealed a focus of neural activity localised to the dentate gyrus which was spatially and temporally aligned to local field potential (LFP) recordings and could be reconstructed reproducibly in all animals with a localisation accuracy of ≤400 â€‹µm (p â€‹< â€‹0.03125, N â€‹= â€‹5). These findings represent the first experimental evidence of the ability of EIT to image neural activity in subcortical structures from the surface of the cortex with high spatiotemporal resolution and suggest that this method may be used for improving understanding of functional connectivity between cortico-hippocampal networks in both physiological and pathophysiological states.

Bi-Frequency Symmetry Difference EIT-Feasibility and Limitations of Application to Stroke Diagnosis.

OBJECTIVE: Bi-Frequency Symmetry Difference (BFSD)-EIT can detect, localize and identify unilateral perturbations in symmetric scenes. Here, we test the viability and robustness of BFSD-EIT in stroke diagnosis. METHODS: A realistic 4-layer Finite Element Method (FEM) head model with and without bleed and clot lesions is developed. Performance is assessed with test parameters including: measurement noise, electrode placement errors, contact impedance errors, deviations in assumed tissue conductivity, deviations in assumed anatomy, and a frequency-dependent background. A final test is performed using ischemic patient data. Results are assessed using images and quantitative metrics. RESULTS: BFSD-EIT may be feasible for stroke diagnosis if a signal-to-noise ratio (SNR) of ≥60 dB is achievable. Sensitivity to errors in electrode positioning is seen with a tolerance of only ±5 mm, but a tolerance of up to ±30 mm is possible if symmetry is maintained between symmetrically opposite partner electrodes. The technique is robust to errors in contact impedance and assumed tissue conductivity up to at least ±50%. Asymmetric internal anatomy affects performance but may be tolerable for tissues with frequency-dependent conductivity. Errors in assumed external geometry marginally affect performance. A frequency-dependent background does not affect performance with carefully chosen frequency points or use of multiple frequency points across a band. The Global Left-Hand Side (LHS) & Right-Hand Side (RHS) Mean Intensity metric is particularly robust to errors. CONCLUSION: BFSD-EIT is a promising technique for stroke diagnosis, provided parameters are within the tolerated ranges. SIGNIFICANCE: BFSD-EIT may prove an important step forward in imaging of static scenes such as stroke.

Optimisation of bioimpedance measurements of neuronal activity with an ex vivo preparation of Cancer pagurus peripheral nerves.

BACKGROUND: In mammals, fast neural Electrical Impedance Tomography (EIT) can image the myelinated component of the compound action potentials (CAP) using a nerve cuff. If applied to unmyelinated fibres this has great potential to improve selective neuromodulation ("electroceuticals") to avoid off-target effects. Previously, bioimpedance recordings were averaged from unmyelinated crab leg nerve fibres, but the signal to noise ratio (SNR) needs improving. NEW METHOD: Currently, functional non-invasive neuronal imaging is accomplished through surface electrodes or genetically expressed indicators that provide good spatial, but poor temporal, resolution. Here is an improved method for bioimpedance measurements from a model of unmyelinated fibres to enable optimisation through improvement of the 1) signal processing measurement paradigm, 2) neurophysiology, and 3) electrode-nerve interface. RESULTS: For bioimpedance recordings, the recruitment and necessity of the CAP was quantified and saline significantly improved the SNR. An improved protocol resulted in averaging not being required, as sequentially recorded traces produced bioimpedance changes of -0.232 ± 0.064% that did not show phase or timing related artefacts. COMPARISON WITH EXISTING METHOD: Here, two bioimpedance traces displayed an SNR of ≥3:1, while previously over >100 averages were required with greater inter-experimental variability. 10 paired traces were averaged for an SNR of ≥9:1, or near real-time measurement. CONCLUSIONS: This method facilitates further studies aiming to enable non-invasive localization of fascicular activity in unmyelinated fibres within peripheral nerves. This technique could ultimately produce the first 3-D tomographic images to help guide selective neuromodulation using bioelectric devices.

Investigating the safety of fast neural electrical impedance tomography in the rat brain.

OBJECTIVE: Electrical impedance tomography (EIT) can be used to image impedance changes which arise due to fast electrical activity during neuronal depolarisation and so holds therapeutic potential for improving the localisation of epileptic seizure foci in patients with treatment-resistant epilepsy to aid surgical resection of epileptogenic tissue. Prolonged cortical stimulation may, however, induce neural injury through excitotoxicity and electrochemical reactions at the tissue-electrode interface. The purpose of this work was to assess whether current levels used in fast neural EIT studies induce histologically detectable tissue damage when applied continuously to the rat cerebral cortex. APPROACH: A 57-electrode epicortical array was placed on one or both hemispheres of adult Sprague Dawley rats anaesthetised with isoflurane. In an initial series of experiments, current was injected simultaneously at 10, 25, 50, 75 and 100 µA for 1 h at 1.725 kHz through five electrodes across two epicortical arrays to provide a preliminary indication of the safety of these current levels. Since no obvious cortical damage was observed in these rats, the current level chosen for further investigation was 100 µA, the upper-bound of the range of interest. In a separate series of experiments, 100 µA was applied through a single electrode for 1 h at 1.725 kHz to verify its safety. Following termination of stimulation, brain samples were fixed in formalin and histologically processed with Haematoxylin and Eosin (H&E) and Nissl stains. MAIN RESULTS: Histological analysis revealed that continuous injection of 100 µA current, equating to a current density of 354 Am-2, into the rat cortex at 1.725 kHz does not cause cortical tissue damage or any alterations to neuronal morphology. SIGNIFICANCE: The safety of current injections during typical EIT protocols for imaging fast neural activity have been validated. The current density established to be safe for continuous application to the cortex, 354 Am-2, exceeds the present safety limit of 250 Am-2 which has been complied with to date, and thus encourages the application of more intensified fast neural EIT protocols. These findings will aid protocol design for future clinical and in vivo EIT investigations aimed at imaging fast neural activity, particularly in situations where the signal-to-noise ratio is considerably reduced.

Simultaneous EIT and EEG using frequency division multiplexing.

OBJECTIVE: Methods have previously been reported for simultaneous EIT and EEG recording, but these have relied on post-hoc signal processing to remove switching artefacts from the EEG signal and require dedicated hardware filters and the use of separate EEG and EIT electrodes. This work aims to demonstrate that an uncorrupted EEG signal can be collected simultaneously with EIT data by using frequency division multiplexing (FDM), and to show that the EIT data provides useful information when compared to EEG source localisation. APPROACH: A custom FDM EIT current source was created and evaluated in resistor phantom and neonatal head tank experiments, where a static and dynamic perturbation was imaged. EEG and EIT source localisation were compared when an EEG dipole was placed in the tank. EEG and EIT data were collected simultaneously in a human volunteer, using both a standard EEG and a visual evoked potential (VEP) paradigms. MAIN RESULTS: Differences in EEG and VEP collected with and without simultaneous EIT stimulation showed no significant differences in amplitude, latency or PSD (p-values >0.3 in all cases). Compared with EEG source localisation, EIT reconstructions were more accurately able to reconstruct both the centre of mass and volume of a perturbation. SIGNIFICANCE: The reported method is suitable for collecting EIT in a clinical setting, without disrupting the clinical EEG or requiring additional measurement electrodes, which lowers the barrier to entry for data collection. EIT collection can be integrated with existing clinical workflows in EEG/ECoG, with minimal disruption to the patient or clinical team.

Bi-frequency symmetry difference electrical impedance tomography-a novel technique for perturbation detection in static scenes.

OBJECTIVE: A novel method for the imaging of static scenes using electrical impedance tomography (EIT) is reported with implementation and validation using numerical and phantom models. The technique is applicable to regions featuring symmetry in the normal case, asymmetry in the presence of a perturbation, and where there is a known, frequency-dependent change in the electrical conductivity of the materials in the region. APPROACH: The stroke diagnostic problem is used as a motivating sample application. The head is largely symmetrical across the sagittal plane. A haemorrhagic or ischaemic lesion located away from the sagittal plane will alter this natural symmetry, resulting in a symmetrical imbalance that can be detected using EIT. Specifically, application of EIT stimulation and measurement protocols at two distinct frequencies detects deviations in symmetry if an asymmetrically positioned lesion is present, with subsequent identification and localisation of the perturbation based on known frequency-dependent conductivity changes. Anatomically accurate computational models are used to demonstrate the feasibility of the proposed technique using different types, sizes, and locations of lesions with frequency-dependent (or independent) conductivity. Further, a realistic experimental head phantom is used to validate the technique using frequency-dependent perturbations emulating the key numerical simulations. MAIN RESULTS: Lesion presence, type, and location are detectable using this novel technique. Results are presented in the form of images and corresponding robust quantitative metrics. Better detection is achieved for larger lesions, those further from the sagittal plane, and when measurements have a higher signal-to-noise ratio. SIGNIFICANCE: Bi-frequency symmetry difference EIT is an exciting new modality of EIT with the ability to detect deviations in the symmetry of a region that occur due to the presence of a lesion. Notably, this modality does not require a time change in the region and thus may be used in static scenarios such as stroke detection.

Electrode fabrication and interface optimization for imaging of evoked peripheral nervous system activity with electrical impedance tomography (EIT).

OBJECTIVE: Non-invasive imaging techniques are undoubtedly the ideal methods for continuous monitoring of neural activity. One such method, fast neural electrical impedance tomography (EIT) has been developed over the past decade in order to image neural action potentials with non-penetrating electrode arrays. APPROACH: The goal of this study is two-fold. First, we present a detailed fabrication method for silicone-based multiple electrode arrays which can be used for epicortical or neural cuff applications. Secondly, we optimize electrode material coatings in order to achieve the best accuracy in EIT reconstructions. MAIN RESULTS: The testing of nanostructured electrode interface materials consisting of platinum, iridium oxide, and PEDOT:pTS in saline tank experiments demonstrated that the PEDOT:pTS coating used in this study leads to more accurate reconstruction dimensions along with reduced phase separation between recording channels. The PEDOT:pTS electrodes were then used in vivo to successfully image and localize the evoked activity of the recurrent laryngeal fascicle from within the cervical vagus nerve. SIGNIFICANCE: These results alongside the simple fabrication method presented here position EIT as an effective method to image neural activity.

Deployable, Variable Stiffness, Cable Driven Robot for Minimally Invasive Surgery.

Minimally Invasive Surgery (MIS) imposes a trade-off between non-invasive access and surgical capability. Treatment of early gastric cancers over 20 mm in diameter can be achieved by performing Endoscopic Submucosal Dissection (ESD) with a flexible endoscope; however, this procedure is technically challenging, suffers from extended operation times and requires extensive training. To facilitate the ESD procedure, we have created a deployable cable driven robot that increases the surgical capabilities of the flexible endoscope while attempting to minimize the impact on the access that they offer. Using a low-profile inflatable support structure in the shape of a hollow hexagonal prism, our robot can fold around the flexible endoscope and, when the target site has been reached, achieve a 73.16% increase in volume and increase its radial stiffness. A sheath around the variable stiffness structure delivers a series of force transmission cables that connect to two independent tubular end-effectors through which standard flexible endoscopic instruments can pass and be anchored. Using a simple control scheme based on the length of each cable, the pose of the two instruments can be controlled by haptic controllers in each hand of the user. The forces exerted by a single instrument were measured, and a maximum magnitude of 8.29 N observed along a single axis. The working channels and tip control of the flexible endoscope remain in use in conjunction with our robot and were used during a procedure imitating the demands of ESD was successfully carried out by a novice user. Not only does this robot facilitate difficult surgical techniques, but it can be easily customized and rapidly produced at low cost due to a programmatic design approach.